Exposure apparatus

ABSTRACT

This invention provides an exposure apparatus capable of properly reading an electrical signal from a photoelectric sensor by using the time interval between emission pulses even at a high emission frequency of the light source. A photoelectric sensor attached to an exposure apparatus which exposes a substrate to a pulse beam emitted by a light source for generating a pulse beam has a plurality of photoelectric converters ( 29 - 1 - 29 - n ). The photoelectric converters ( 29 - 1 - 29 - n ) are divided into a plurality of blocks. While charges are read from each block by using one time interval between pulse beams, charges in all the photoelectric converters ( 29 - 1 - 29 - n ) are read by using a plurality of time intervals between pulse beams.

FIELD OF THE INVENTION

[0001] The present invention relates to an exposure apparatus suitablefor manufacturing a device such as a semiconductor device or liquidcrystal display device.

BACKGROUND OF THE INVENTION

[0002] An exposure apparatus which transfers the pattern of a mastersuch as a reticle onto a photosensitive material applied to a substratesuch as a wafer or glass plate is used to manufacture a device such as asemiconductor device or liquid crystal display device byphotolithography.

[0003] In general, a photosensitive material applied to a wafer has apredetermined proper exposure amount. In a conventional exposureapparatus, a beam splitter is arranged in an illumination optical systemfor illumination light. The light quantity of part of illumination lightsplit by the beam splitter is monitored by a photoelectric sensor(integrated exposure amount sensor), thereby indirectly monitoring theexposure amount of the wafer. When the exposure amount of the waferreaches a proper exposure amount, exposure to the current shot region ofthe wafer is stopped to control the exposure amount.

[0004] In such exposure apparatus, the relationship between theilluminance on the wafer and an output from the integrated exposureamount sensor in the illumination optical system must be measured inadvance. For this measurement, a photoelectric sensor for measuring theilluminance on the wafer is generally set on a stage which holds thewafer. The photoelectric sensor on the stage is often used to measurethe illuminance uniformity of exposure light incident on the wafer via aprojection optical system, and is generally called an illuminanceuniformity sensor.

[0005] The illuminance uniformity sensor is generally a singlephotodiode (light-receiving element or photoelectric converter), or aphotodiode-array or CCD (Charge Coupled Device) comprised of a pluralityof photodiodes. A line or area type photoelectric sensor such as thephotodiode array or CCD stores charges proportional to the incidentlight quantity output from the photodiode in a charge storage(capacitor) within the photoelectric sensor. Stored charges are readfrom the charge storage in accordance with a read command, convertedfrom a current into a voltage, and used for various processes.

[0006] To calibrate an output from the illuminance uniformity sensor, anilluminance meter calibrated in advance is set below the projectionoptical system instead of a wafer, and the illuminance is measured bythe calibration illuminance meter. The illuminance uniformity sensor tobe calibrated is then moved below the projection optical system, theilluminance is similarly measured by the illuminance uniformity sensor,and an output is so adjusted as to be equal to an output from thecalibration illuminance meter.

[0007] As a method of checking whether exposure amount control iscorrectly executed, a predetermined exposure amount is set, and theilluminance uniformity sensor is moved below the projection opticalsystem instead of a wafer. In this state, while exposure amount controlis executed on the basis of an output from the integrated exposureamount sensor, an exposure amount actually incident on the illuminanceuniformity sensor is measured.

[0008] It is a recent trend to use an excimer laser source as anexposure light source in an exposure apparatus which sequentiallyexposes a plurality of shot regions on a wafer by a step & repeat methodusing a so-called stepper. The excimer laser typically has an energydispersion of about 10% for 3σ between output pulses. To achieve adesired exposure amount precision of, e.g., 1% using a light sourcehaving such energy dispersion, a wafer must be irradiated with at least100 pulses to perform integrated exposure. For a small target exposureamount, the illuminance is decreased by a beam attenuation means set inthe illumination optical system so as to make an actual exposure amountfall within the tolerance of the target exposure amount by integratedexposure of, e.g., 100 pulses.

[0009] However, the conventional arrangement requires a wide dynamicrange for the integrated exposure amount sensor in the illuminationoptical system or the illuminance uniformity sensor on the stage. Thisis because these photoelectric sensors must measure light quantitiesranging from a large light quantity which is not attenuated and is usedfor a large exposure amount to a small light quantity which isattenuated by the beam attenuation means and used for a small exposureamount. The front surface of the photoelectric sensor is covered withthe beam attenuation means which adjusts the light quantity such that anoptimal light quantity is incident on the photoelectric sensor. Ingeneral, the beam attenuation means is so set as not to saturate anoutput from the photoelectric sensor even if a maximum light quantity isincident on the photoelectric sensor. When the exposure amount is setsmall and a light quantity incident on the photoelectric sensordecreases, an output from the photoelectric sensor greatly decreases. Asa result, the measurement precision decreases under the influence ofnoise by the dark current of the photoelectric sensor itself, thermalnoise, and the linearity between the incident light quantity and outputof the photoelectric sensor.

[0010] When the illuminance uniformity sensor adopts a line or area typephotoelectric sensor such as a photodiode array or CCD comprised of aplurality of light-receiving elements (photoelectric converters), a longread time is taken to read output signals from all the light-receivingelements. The emission frequency of an excimer laser has recently beenincreased, and lasers having an emission frequency of 4 kHz or morebecome available. Such high-frequency laser has a short time intervalbetween emission pulses, and it becomes difficult to read output signalsfrom all the light-receiving elements within this time interval.

SUMMARY OF THE INVENTION

[0011] The present invention has been made by giving attentionparticularly to the latter problem out of the two problems describedabove, and has as its object to provide an exposure apparatus whicheasily copes with an increase in the emission frequency of a lightsource and, more specifically, an exposure apparatus capable of properlyreading an electrical signal from a photoelectric sensor by using thetime interval between emission pulses even at a high emission frequencyof the light source.

[0012] According to the present invention, an exposure apparatus whichtransfers a pattern onto a substrate by using pulse beams periodically,successively emitted by a light source for generating a pulse beamcomprises a photoelectric array having a plurality of photoelectricconverters which detect pulse beams as electrical signals, and a readcircuit which reads the electrical signals from the plurality ofphotoelectric converters of the photoelectric array. The read circuitstores, in the plurality of photoelectric converters of thephotoelectric array, charges corresponding to light quantities of pulsebeams periodically, successively emitted by the light source to thephotoelectric array, and reads electrical signals from all the pluralityof photoelectric converters by using a plurality of time intervalsbetween the pulse beams while reading electrical signals from some ofthe plurality of photoelectric converters by using each time intervalbetween the pulse beams. With this arrangement, even when the emissionfrequency of the light source increases, an electrical signal can beproperly read from a photoelectric sensor by using the time intervalbetween emission pulses. The obtained electrical signal can be utilizedfor control of the exposure amount, calibration of the exposure controlsystem, or the like. The electrical signal should be interpreted to havethe widest meaning, and the term “electrical signal” includes allelectrical signals such as an analog signal, digital signal, andelectrically expressible numerical information (data).

[0013] According to a preferred aspect of the present invention, theread circuit preferably includes a reset circuit which resets aphotoelectric converter from which an electrical signal has been readevery time an electrical signal is read from the photoelectric array.

[0014] According to another preferred aspect of the present invention,the exposure apparatus preferably further comprises an adder which addselectrical signals read from the same photoelectric converter atdifferent times.

[0015] According to still another preferred aspect of the presentinvention, the number of photoelectric converters from which electricalsignals are read by the read circuit at one time interval between pulsesis preferably determined in accordance with an emission frequency of thelight source. For example, the number of photoelectric converters can bedetermined to a relatively small number for a high emission frequency ofthe light source, and a relatively large number for a low emissionfrequency of the light source. Alternatively, the number ofphotoelectric converters can be determined to as large a number aspossible or a number suitable for data processing within a range inwhich electrical signals can be read at one time interval betweenpulses.

[0016] According to still another preferred aspect of the presentinvention, a count at which charges corresponding to pulse beamsperiodically, successively emitted by the light source to thephotoelectric array are integrated and stored in the plurality ofphotoelectric converters is preferably determined in accordance with anintensity of the pulse beam emitted by the light source. For example,the integration/storage count can be so determined as to operate thephotoelectric array within a dynamic range limited to a predeterminedrange. By the method of limiting the dynamic range, a decrease inmeasurement precision or detection precision by dark current noise ofthe photoelectric array (or photoelectric converter), thermal noise, orthe linearity of the input/output characteristic can be suppressed to adesired level or less.

[0017] According to a typical aspect of the present invention, thephotoelectric array can be arranged on, e.g., a stage which holds thesubstrate. Alternatively, the photoelectric array may be so arranged asto detect a integrated light quantity of a pulse beam split from anoptical path extending from the light source to the substrate.

[0018] According to still another aspect of the present invention, anexposure apparatus which transfers a pattern onto a substrate by usingpulse beams periodically, successively emitted by a light source forgenerating a pulse beam comprises a photoelectric sensor which detects apulse beam as an electrical signal, and a read circuit which reads theelectrical signal from the photoelectric sensor. The number of pulsescorresponding to charges to be stored in the photoelectric sensorbetween one read operation and next read operation by the read circuitis determined in accordance with an intensity of the pulse beam emittedby the light source.

[0019] According to still another aspect, the photoelectric sensor canbe typically arranged on a stage which holds the substrate.Alternatively, the photoelectric sensor may be so arranged as to detecta integrated light quantity of a pulse beam split from an optical pathextending from the light source to the substrate.

[0020] In the above inventions or preferred aspects, the light source ispreferably an excimer laser.

[0021] The advantages of the exposure apparatus according to the presentinvention can be reflected even in various devices which can bemanufactured by the exposure apparatus. As an application example of theexposure apparatus according to the present invention, the exposureapparatus of the present invention can be used in a transfer step in adevice manufacturing method using lithography including a transfer stepof transferring a pattern onto a photosensitive agent applied to asubstrate, and a developing step of developing the photosensitive agent.

[0022] Other features and advantages of the present invention will beapparent from the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

[0024]FIG. 1 is a view showing the schematic arrangement of an exposureapparatus according to a preferred embodiment of the present invention;

[0025]FIG. 2 is a diagram showing the basic structure of a integratedexposure amount sensor and illuminance uniformity sensor (photoelectricsensors) in FIG. 1;

[0026]FIG. 3 is a diagram showing an example of the arrangement of theilluminance uniformity sensor (photoelectric sensor) in which aplurality of photoelectric converters are arrayed;

[0027]FIG. 4 is a view showing stored charges and read of a photodiodearray;

[0028]FIG. 5 is a view showing stored charges and divisional read of thephotodiode array;

[0029]FIG. 6 is a flow chart showing the manufacturing flow of amicrodevice; and

[0030]FIG. 7 is a flow chart showing the detailed flow of a waferprocess in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Preferred embodiments of the present invention will be describedbelow with reference to the accompanying drawings.

[0032]FIG. 1 is a view showing the schematic arrangement of an exposureapparatus according to a preferred embodiment of the present invention.The exposure apparatus shown in FIG. 1 can be implemented as a step &repeat exposure apparatus (so-called stepper) or a step & scan exposureapparatus (so-called scanner). A light source 1 generates a pulse beamas illumination light, and is typically an excimer laser. The lightsource 1 generates a pulse beam in accordance with an emission commandsent from a main control system 25. The pulse beam means light having apulse waveform along the time axis.

[0033] A beam attenuation mechanism 28 adjusts the light quantity ofillumination light so as to adjust the intensity (illuminance) of lightincident on a wafer 11. The beam attenuation mechanism 28 has, e.g., aturret structure which holds a plurality of neutral-density filtershaving different transmittances, and switches the beam attenuation ratioby the filters. For example, the beam attenuation mechanism 28 can beequipped with 25 neutral-density filters whose beam attenuation ratiochanges by 10%. In this case, the transmittances of the neutral-densityfilters are 100%, 90%, 81%, 72.9%, 65.6%, 59%, 53.1%, 47.8%, 43%, 38.7%,34.9%, 31.4%, 28.2%, 25.4%, 22.9%, 20.6%, 18.5%, 16.7%, 15%, 13.5%,12.2%, 11%, 9.8%, 8.9%, and 8.0%. The beam attenuation ratio is a valueobtained by subtracting the transmittance from 100%.

[0034] A beam shaping optical system 2 shapes illumination light emittedby the excimer laser 1 into a parallel beam having a predeterminedsectional shape. A quarter-wave plate 3 converts linearly polarizedillumination light having passed through the beam shaping optical system2 into circularly polarized illumination light. Circularly polarizedillumination light is reflected by a reflecting mirror 4 to enter afly-eye lens 5. Many light source images are formed on the exit surfaceof the fly-eye lens 5, making the illuminance distribution ofillumination light uniform.

[0035] A beam splitter 6 transmits most of illumination light havingpassed through the fly-eye lens 5, and reflects the remaining part ofillumination light to a integrated exposure amount sensor 14 via acondenser lens 12. Illumination light having passed through the beamsplitter 6 illuminates a reticle (master) 9 via an illumination opticalsystem 7 with a uniform illuminance distribution. In this embodiment, areflecting mirror 8 is arranged in the illumination optical system 7 todeflect illumination light.

[0036] A pattern formed on the reticle 9 is projected onto the wafer(substrate) 11 via a projection optical system 10 to expose the wafer 11to pattern light.

[0037] Light reflected by the beam splitter 6 is condensed on thelight-receiving surface of the integrated exposure amount sensor 14 bythe condenser lens 12. The integrated exposure amount sensor 14 can beformed by a photoelectric sensor which converts an optical signal intoan electrical signal. As is well known, the photoelectric sensorincludes a photodiode or a CCD constituted by integrating photodiodes.

[0038] An illuminance uniformity sensor 18 for detecting the illuminanceuniformity on the wafer 11 is mounted on a stage 17 which holds andmoves the wafer 11. The illuminance uniformity sensor 18 can also beformed by a photoelectric sensor.

[0039]FIG. 2 is a diagram showing the basic structure of the integratedexposure amount sensor 14 and illuminance uniformity sensor 18, i.e.,photoelectric sensors in FIG. 1. The photoelectric sensor (integratedexposure amount sensor 14 or illuminance uniformity sensor 18) iscomprised of a single light-receiving element (photoelectric converter).The photoelectric sensor can be formed by a plurality of light-receivingelements (photoelectric converters) which are arranged one- ortwo-dimensionally.

[0040] A photodiode 15 serving as a light-receiving element is typicallyarranged such that its light-receiving surface coincides with a positionflush with or conjugate to the exposure surface of the wafer 11 (FIG.1). The front surface of the photodiode 15 is covered with aneutral-density filter 27 which transmits an optimal light quantity tothe photodiode 15 when a neutral-density filter having a transmittanceof 100% (beam attenuation ratio of 0%) is selected in the beamattenuation mechanism 28. Charges (current) proportional to an incidentlight quantity generated by the photodiode 15 are stored in a chargestorage (capacitor) 19. An output current from the charge storage 19 isconverted into a voltage by a current-to-voltage converter 16, and thevoltage is applied as exposure amount data 21 (23) to the main controlsystem 25. The charge storage 19 receives a charge reset signal 20 (22)from the main control system 25.

[0041] Referring back to FIG. 1, check operation for integrated exposureamount control will be explained. Letting D (J/m²) be the set exposureamount (target exposure amount), P (W/m²) be the illuminance on a wafersurface per pulse of a pulse beam generated by the light source 1, F(pls/sec) be the laser emission frequency, and M (pls) be the emissionpulse count, the set exposure amount D is given by equation (1), and theemission pulse count M for obtaining the set exposure amount is given byequation (2):

D(J/m²)=P (W/m²)·M(pls)/F(pls/sec)   (1)

M(pls)=D−F/P   (2)

[0042] In check of integrated exposure amount control, the illuminanceuniformity sensor 18 is moved below the projection optical system 10 inplace of a wafer, and integrated exposure amount control is executed onthe basis of an output from the integrated exposure amount sensor 14 soas to obtain the set exposure amount. During this period, the lightquantities of all pulse beams incident on the illuminance uniformitysensor 18 are integrated using the illuminance uniformity sensor 18 toobtain the integrated exposure amount. The integrated exposure amount iscompared with the set exposure amount to calculate the control precisionof the integrated exposure amount.

[0043] According to the first embodiment of the present invention, thepulse count by which integrated storage is executed in the illuminanceuniformity sensor 18 is switched in accordance with the transmittance ofthe beam attenuation mechanism 28, i.e., the intensity of light incidenton the illuminance uniformity sensor 18. More specifically, the pulsecount is switched as follows. The following operation can be controlledby the main control system 25.

[0044] When a neutral-density filter having a transmittance of 100% isselected in the beam attenuation mechanism 28, integration of a pulsebeam incident on the illuminance uniformity sensor 18 is executed asfollows. Before emission of the light source (excimer laser) 1, the maincontrol system 25 sends to the charge storage 19 of the illuminanceuniformity sensor 18 the charge reset command signal 22 for resettingstored charges. The light source 1 is then caused to emit a pulse beamof one pulse. At this time, charges proportional to the light quantityof the pulse beam are generated in the photodiode 15, and stored in thecharge storage 19. Stored charges are converted into a voltage by thecurrent-to-voltage converter 16, and the voltage is sent as exposureamount data 23 to the main control system 25. The main control system 25sends the charge reset command signal 22 to the charge storage 19. Inresponse to this, charges stored in the charge storage 19 are reset. Aseries of operations using one pulse as a unit are repeated by apredetermined pulse count to sequentially send exposure amount data 23to the main control system 25. All the exposure amount data 23 are addedby an adder 25 a in the main control system 25 to obtain a integratedexposure amount.

[0045] When a neutral-density filter having a transmittance of 47.8% isselected in the beam attenuation mechanism 28, integration of a pulsebeam incident on the illuminance uniformity sensor 18 is executed asfollows. Before emission of the light source (excimer laser) 1, the maincontrol system 25 sends to the charge storage 19 the charge resetcommand signal 22 for resetting stored charges. The light source 1 isthen caused to emit a pulse beam of one pulse. At this time, chargesproportional to the light quantity of the pulse beam are generated inthe photodiode 15, and stored in the charge storage 19. The light source1 is caused to emit a pulse beam of one pulse without sending the chargereset signal 22 to the charge storage 19. Charges generated in thephotodiode 15 are integrated to previous charges in the charge storage19. Since the light quantity incident on the illuminance uniformitysensor 18 is attenuated to 47.8%, charges of two pulses are integratedin the illuminance uniformity sensor 18 to obtain almost the same chargeamount as that upon selecting a neutral-density filter having atransmittance of 100%. Exposure amount data 23 of the two pulses is sentto the main control system 25. The main control system 25 sends thecharge reset command signal 22 to the charge storage 19. In response tothis, charges (two pulses) stored in the charge storage 19 are reset. Aseries of operations using two pulses as a unit are repeated by apredetermined pulse count to sequentially send exposure amount data 23to the main control system 25. All the exposure amount data 23 are addedby the adder 25 a in the main control system 25 to obtain a integratedexposure amount.

[0046] When a neutral-density filter having a transmittance of 25.4% isselected in the beam attenuation mechanism 28, charges, of four pulsesare integrated and stored in the illuminance uniformity sensor 18,thereby storing almost the same charge amount as that upon selecting aneutral-density filter having a transmittance of 100%. A series ofoperations using four pulses as a unit are repeated by a predeterminedpulse count to sequentially send exposure amount data 23 to the maincontrol system 25. All the exposure amount data 23 are added by theadder 25 a in the main control system 25 to obtain a integrated exposureamount.

[0047] In this manner, according to the first embodiment of the presentinvention, the pulse count by which storage accompanied by integrationis executed in the charge storage 19 is changed in accordance with thebeam attenuation ratio set by the beam attenuation mechanism 28 in theillumination optical system, i.e., the intensity of light incident onthe illuminance uniformity sensor 18. As a result, an output from thecharge storage 19 of the illuminance uniformity sensor 18 can be limitedto a narrow dynamic range, substantially preventing the influence ofnoise by the dark current of the illuminance uniformity sensor 18itself, thermal noise, and the linearity between the incident lightquantity and output of the illuminance uniformity sensor 18.

[0048] The method of changing the pulse count by which storageaccompanied by integration is executed in accordance with the intensity(illuminance) of light incident on the photoelectric sensor can beapplied not only to check of the integrated exposure amount but also toevaluation of illuminance uniformity.

[0049] This photoelectric sensor control method can be applied not onlyto control of the illuminance uniformity sensor 18 but also to theintegrated exposure amount sensor 14. In this case, the method can beapplied not only to actual exposure of a wafer, but also to check ofintegrated exposure amount control or evaluation of the transmittance ofan optical system between the integrated exposure amount sensor and theilluminance uniformity sensor.

[0050] The photoelectric sensor control method can be applied not onlyto an exposure apparatus, but also to any apparatus having a lightsource for generating a pulse beam and a function of changing theintensity of a pulse beam incident on a photoelectric sensor.

[0051] As the second embodiment of the present invention, a method ofsolving the problem of the read time in the use of a photoelectricsensor in which light-receiving elements (photoelectric converters) arearrayed one- or two-dimensionally will be explained. This problem hasbeen described in “BACKGROUND OF THE INVENTION”, but will be explainedagain with reference to FIG. 3.

[0052] A photoelectric sensor in which a plurality of photoelectricconverters are arrayed will be described. FIG. 3 is a diagram showing anexample of the arrangement of an illuminance uniformity sensor 18 inwhich a plurality of photoelectric converters are arrayed. Theilluminance uniformity sensor 18 shown in FIG. 3 has a photodiode array(photoelectric array) 29, and the array 29 is comprised of first to nthphotoelectric converters 29-1 to 29-n. Each photoelectric converter canbe formed by a photodiode 15 and charge storage 19 shown in FIG. 2.

[0053] The charge storages of the photoelectric converters 29-1 to 29-nare connected to charge transmission switches 30-1 to 30-n fortransmitting charges stored in the charge storages to acurrent-to-voltage converter 16. The switches 30-1 to 30-n aresequentially turned on to sequentially supply charges stored in thecharge storages of the photoelectric converters 29-1 to 29-n to thecurrent-to-voltage converter 16. Stored charges flow into thecurrent-to-voltage converter 16 to reset a charge storage which hasemitted stored charges.

[0054] The charge transmission switches 30-1 to 30-n are sequentiallyturned on by a shift register (scanning circuit) 31 by a method to bedescribed,later. Charges stored in an ON charge storage are convertedinto a voltage by the current-to-voltage converter 16, and the voltageis output as exposure amount data 23 to a main control system 25. Thecharge transmission switches 30-1 to 30-n and the shift register 31constitute all or part of a read circuit.

[0055] In the second embodiment, the exposure amount data 23 is ananalog voltage signal. This signal is A/D-converted by an A/D converter(not shown) in the main control system 25, written in a memory 25 m, andthen processed.

[0056] For deeper understanding of the second embodiment, a problem inthe use of a photoelectric sensor array will be explained with referenceto FIG. 4. FIG. 4 schematically shows pulse emission of a light source 1in the exposure apparatus and corresponding operation of the photodiodearray (photoelectric array) 29.

[0057] (a) of FIG. 4 schematically shows a method of reading chargesevery emission of one pulse. In (a) of FIG. 4, each  represents chargesgenerated in the photodiode in accordance with emission of one pulse bythe light source 1 such as an excimer laser. Charges are externallytransferred via the current-to-voltage converter 16 by sequentiallyturning on the charge transmission switches 30-1 to 30-n in a directionindicated by an arrow.

[0058] The dots  on the right side in (a) of FIG. 4 represent datawhich are read from the photoelectric sensor 18, A/D-converted, andstored in the memory 25 m. Read of all signals (charges) in thephotodiode array 29 by the general read method takes a read time givenby equation (3):

Read time (T 1)=(charge read time per photoelectric converter)×(numberof photoelectric converters)   (3)

[0059] (b) of FIG. 4 shows a method of reading charges of two pulses. In(b) of FIG. 4,  represents charges stored by emission of the firstpulse, and ◯ represents charges stored by emission of the second pulse.More specifically, in (b) of FIG. 4, charges corresponding to pulsebeams of two pulses generated by the light source 1 are stored in thephotoelectric converters 29-1 to 29-n of the photodiode array 29, andthen read. In the example of (b) of FIG. 4, charges in the photoelectricconverters 29-1 to 29-n of the photodiode array 29 are read every timeemission of two pulses ends. Read must be executed before the start ofthe next pulse emission, and the read time (T1) must be shorter than thetime interval of pulse emission. That is, the time permitted as the readtime (T1) is equal between (a) and (b) of FIG. 4.

[0060] Assuming that the charge read time of one photoelectric converteris 2 μsec and the number of photoelectric converters is 256, the readtime (T1) taken to read charges in all the photoelectric converters is 2μsec×256=0.512 msec.

[0061] When the emission frequency of the light source 1 is 1,000 Hz,the emission pulse cycle is 1 msec, and 256 signals can be read with atemporal margin within the time interval between pulses, as shown in (a)of FIG. 4. However, when the emission frequency of the light source 1 is2,000 Hz, the emission pulse cycle is 0.5 msec, and signals cannot beread within the time interval between pulses. That is, as the emissionfrequency of the light source 1 increases, it becomes more difficult toread signals from all the photoelectric converters within the timeinterval of pulse emission.

[0062] Under this circumstance, the second embodiment provides a readmethod as shown in FIG. 5. In FIG. 5, the number of photoelectricconverters is 16 (i.e., n=16) for descriptive convenience. In FIG. 5,the dots  numbered “1” represent charges by the first pulse; thecircles ◯ numbered “2”, charges by the second pulse; the dots  numbered“3”, charges by the third pulse; and the circles ◯ numbered “4”, chargesby the fourth pulse.

[0063] Before emission of the light source 1 such as an excimer laser,the main control system 25 sends to the charge storages of thephotoelectric converters 29-1 to 29-16 a charge reset command signal 22for resetting stored charges. As shown in (a), charges (charges numbered“1”) are stored by a pulse beam of the first pulse from the light source1 such as an excimer laser. The shift register 31 is then driven to readcharges from the photoelectric converters 29-1 to 29-4 serving as part(first block) of the array 29. Charges are stored at the first to fourthaddresses in the memory 25 m, and driving of the shift register 31 issuspended.

[0064] As shown in (b), charges (charges numbered “2”) are stored by apulse beam of the second pulse from the light source 1. Driving of theshift register 31 restarts to read charges from the photoelectricconverters 29-5 to 29-8 serving as part (second block) of the array 29.Charges are stored at the fifth to eighth addresses in the memory 25 m.

[0065] As shown in (c), charges (charges numbered “3”) are stored by apulse beam of the third pulse from the light source 1. Driving of theshift register 31 restarts to read charges from the photoelectricconverters 29-9 to 29-12 serving as part (third block) of the array 29.Charges are stored at the ninth to 12th addresses in the memory 25 m.

[0066] As shown in (d), charges (charges numbered “4”) are stored by apulse beam of the fourth pulse from the light source 1. Driving of theshift register 31 restarts to read charges from the photoelectricconverters 29-13 to 29-16 serving as part (fourth block) of the array29. Charges are stored at the 13th to 16th addresses in the memory 25 m.

[0067] The operation from (a) to (d) is repeated till the end ofemission from the excimer laser.

[0068] As shown in (e), charges in the photoelectric converters 29-1 to29-4 are read without emitting light from the light source 1. Read dataare added to data stored at the first to fourth addresses in the memory25 m, and stored again at these addresses. Similarly, as shown in (f)and (g), charges in the photoelectric converters 29-5 to 29-8 and 29-9to 29-12 are read without emitting light from the light source 1. Readdata are added to data stored at the fifth to eighth addresses and theninth to 12th addresses in the memory 25 m, and stored again at theseaddresses.

[0069] By the above sequence, exposure amount data representing thecumulate light quantity of the pulse beams of the four pulses stored inthe photoelectric converters 29-1 to 29-n of the photodiode array 29 isstored in the memory 25 m.

[0070] In read by dividing 256 photoelectric converters into four (inFIG. 4, dividing 16 photoelectric converters into four), the data readtime (T2) per pulse from the light source 1 is given by

2 μsec×256/4=0.128 msec

[0071] This time is much shorter than a pulse interval of 0.5 msecobtained when the emission frequency of the light source 1 is set to2,000 Hz. Thus, charges in all the photoelectric converters of a blocksubjected to read (one of the four divided blocks) can be read asexposure amount data by using the time interval between pulses. For ahigh emission frequency of the light source 1, the division number ofthe photodiode array 29 in read is increased. An increase in divisionnumber means a decrease in the number of photoelectric converterssubjected to read at one time interval between pulse beams.

[0072] As described above, according to the second embodiment, whetherto read charges by dividing the photodiode array 29 and further thedivision number in divisional read are determined in accordance with theemission frequency of the light source 1. Even if the emission frequencyincreases, exposure amount data can be obtained from all thephotoelectric converters of the phototransistor array by using aplurality of time intervals between pulse beams while obtaining exposureamount data from some photoelectric converters of the phototransistorarray by using each time interval between pulse beams. In other words,the second embodiment changes or determines the read method of thephotodiode array 29 so as to obtain necessary exposure amount data inaccordance with the emission frequency of the light source 1. Thedivision number (or the number of photoelectric converters subjected toread at one time interval between pulse beams) or the read method isdetermined and changed by the main control system 25 in accordance withthe emission frequency of the light source 1.

[0073] The method of changing the photodiode array read method inaccordance with the emission frequency of a pulse beam can be appliednot only to an exposure apparatus, but also to any apparatus whichmeasures a pulse beam by using a photodiode array.

[0074] The technical concept described as the first embodiment can becombined with the technical concept described as the second embodiment.More specifically, also in the second embodiment, similar to the firstembodiment, the pulse count by which integration and storage areexecuted can be changed in accordance with the intensity of lightincident on the photoelectric sensor to make an output from thephotoelectric sensor fall within a limited dynamic range. In this case,a necessary dynamic range can be widened in accordance with an increasein the division number of photoelectric sensor in read.

[0075] An embodiment of a device production method using theabove-described exposure apparatus or exposure method will be described.FIG. 6 is a flow chart showing the manufacturing flow of a microdevice(semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD,a thin-film magnetic head, a micromachine, or the like). In step 1(circuit design), a device pattern is designed. In step 2 (maskformation), a mask having the designed pattern is formed. In step 3(wafer formation), a wafer is formed using a material such as silicon orglass. In step 4 (wafer process) called a pre-process, an actual circuitis formed on the wafer by lithography using the prepared mask and wafer.Step 5 (assembly) called a post-process is the step of forming asemiconductor chip by using the wafer formed in step 4, and includes anassembly process (dicing and bonding) and packaging process (chipencapsulation). In step 6 (inspection), the semiconductor devicemanufactured in step 5 undergoes inspections such as an operationconfirmation test and durability test. After these steps, thesemiconductor device is completed and shipped (step 7).

[0076]FIG. 7 is a flow chart showing the detailed flow of the waferprocess. In step 11 (oxidation), the wafer surface is oxidized. In step12 (CVD) an insulating film is formed on the wafer surface. In step 13(electrode formation), an electrode is formed on the wafer by vapordeposition. In step 14 (ion implantation), ions are implanted in thewafer. In step 15 (resist processing), a photosensitive agent is appliedto the wafer. In step 16 (exposure), the wafer is exposed to the circuitpattern of the mask by the above-mentioned exposure apparatus having theintegrated exposure amount measurement device. In step 17 (developing),the exposed wafer is developed. In step 18 (etching), the resist isetched except the developed resist image. In step 19 (resist removal),an unnecessary resist after etching is removed. These steps are repeatedto form multiple circuit patterns on the wafer.

[0077] The present invention can provide an exposure apparatus whicheasily copes with an increase in the emission frequency of a lightsource and, more specifically, an exposure apparatus capable of properlyreading an electrical signal from a photoelectric sensor by using thetime interval between emission pulses even at a high emission frequencyof the light source.

[0078] As many apparently widely different embodiments of the presentinvention can be made without departing from the spirit and scopethereof, it is to be understood that the invention is not limited to thespecific embodiments thereof except as defined in the claims.

What is claimed is:
 1. An exposure apparatus which transfers a patternonto a substrate by using pulse beams periodically, successively emittedby a light source for generating a pulse beam, comprising: aphotoelectric array having a plurality of photoelectric converters whichdetect pulse beams as electrical signals; and a read circuit which readsthe electrical signals from the plurality of photoelectric converters ofsaid photoelectric array, wherein said read circuit stores, in the,plurality of photoelectric converters of said photoelectric array,charges corresponding to light quantities of pulse beams periodically,successively emitted by the light source to said photoelectric array,and reads electrical signals from all the plurality of photoelectricconverters by using a plurality of time intervals between the pulsebeams while reading electrical signals from some of the plurality ofphotoelectric converters by using each time interval between the pulsebeams.
 2. The apparatus according to claim 1, wherein said read circuitincludes a reset circuit which resets a photoelectric converter fromwhich an electrical signal has been read every time an electrical signalis read from said photoelectric array.
 3. The apparatus according toclaim 1, further comprising an adder which adds electrical signals readfrom the same photoelectric converter at different times.
 4. Theapparatus according to claim 1, wherein the number of photoelectricconverters from which electrical signals are read by said read circuitat one time interval between pulses is determined in accordance with anemission frequency of the light source.
 5. The apparatus according toclaim 4, wherein the number of photoelectric converters is determined toa relatively small number for a high emission frequency of the lightsource, and a relatively large number for a low emission frequency ofthe light source.
 6. The apparatus according to claim 1, wherein a countat which charges corresponding to pulse beams periodically, successivelyemitted by the light source to said photoelectric array are integratedand stored in the plurality of photoelectric converters is determined inaccordance with an intensity of the pulse beam emitted by the lightsource.
 7. The apparatus according to claim 1, wherein saidphotoelectric array is arranged on a stage which holds the substrate. 8.The apparatus according to claim 1, wherein said photoelectric array isso arranged as to detect a integrated light quantity of a pulse beamsplit from an optical path extending from the light source to thesubstrate.
 9. An exposure apparatus which transfers a pattern onto asubstrate by using pulse beams periodically, successively emitted by alight source for generating a pulse beam, comprising: a photoelectricsensor which detects a pulse beam as an electrical signal; and a readcircuit which reads the electrical signal from said photoelectricsensor, wherein the number of pulses corresponding to charges to bestored in said photoelectric sensor between one read operation and nextread operation by said read circuit is determined in accordance with anintensity of the pulse beam emitted by the light source.
 10. Theapparatus according to claim 9, wherein said photoelectric sensor isarranged on a stage which holds the substrate.
 11. Theapparatus-according to claim 9, wherein said photoelectric sensor is soarranged as to detect a integrated light quantity of a pulse beam splitfrom an optical path extending from the light source to the substrate.12. A device manufacturing apparatus comprising: a transfer step oftransferring a pattern onto a photosensitive agent applied to asubstrate by using an exposure apparatus defined in claim 1; and adeveloping step of developing the photosensitive agent.
 13. A devicemanufacturing apparatus comprising: a transfer step of transferring apattern onto a photosensitive agent applied to a substrate by using anexposure apparatus defined in claim 9; and a developing step ofdeveloping the photosensitive agent.